How much smaller is the diffusivity of a molecule in the retina as opposed to the vitreous of the eye?

Question

I'm interested in the diffusivity of macromolecules inside the mammalian retina, relative to the vitreous. For example is the diffusion coefficient for a macromolecule (protein, 50-150 kDa for example) 10 or 100 times smaller in the retina than the vitreous? The diffusion coefficient for such a macromolecule is about 10^(-6) cm^2/sec in the vitreous - roughly that of a protein in water. I can't seem to find any information on how much smaller it would be in the retina, a tightly packed tissue.

Answer 1

Great question! It would likely be similar to any other epithelial tissue. If you look, the retina is actually composed of retinal epithelial cells. Epithelial cells are found at many sites in the body - your skin. There are very specific types of bonds between cells that you've learned about in other biology classes that alter how things can or cannot cross a barrier. Additionally, there are bonds that hold cells to the tissue around them. These are things like tight junctions, desmosomes, hemi-desmosones, adherens junctions etc. Then you have to factor in transporters on the cells that may move the molecule into or across the cell, you have to consider what type of molecule you are looking at. A small inorganic ion can diffuse simply between the cells with water. Large molecules are very different. Try looking at how those diffuse across a cell membrane, that will give you a much better answer.